1. Field
The present invention relates to methods and apparatus for cleaning a photolithographic substrate, more particularly, methods and apparatus for cleaning adhesive residue on a photolithographic substrate in the manufacture of integrated circuits.
2. Background of the Related Art
The increasing circuit densities have placed additional demands on processes used to fabricate semiconductor devices. For example, as circuit densities increase, the widths of vias, contacts and other features, as well as the dielectric materials between them, decrease to sub-micron dimensions, whereas the thickness of the dielectric layers remains substantially constant, with the result that the aspect ratios for the features, i.e., their height divided by width, increases. Reliable formation of high aspect ratio features is important to the success of sub-micron technology and to the continued effort to increase circuit density and quality of individual substrates.
Photolithography is a technique used to form precise patterns and structures on the substrate surface and then the patterned substrate surface is etched to form the desired device or features. The photolithographic technique utilizes a photolithographic substrate, such as a reticle, which has corresponding configures of features desired to be transferred to a target substrate, such as a semiconductor wafer. A light source emitting ultraviolet (UV) light or deep ultraviolet (DUV) light is transmitted through the photomask substrate to expose photoresist disposed on the substrate. Generally, the exposed resist material is removed by a chemical process to expose the underlying substrate material. The exposed underlying substrate material is then etched to form the features in the substrate surface while the retained resist material remains as a protective coating for the unexposed underlying substrate material.
An integrated circuit manufacturing process may require several photolithography processes performed at different stages. One reticle may be repeatedly used to reproducibly imprint thousands of substrates. Typically, while performing the photolithography process, a pellicle is used to protect the reticle from particle contamination. Pellicle is a thin transparent membrane which allows lights and radiation to pass therethrough to the recitle. One significant issue for current deep UV lithography is progressive defect (e.g., haze) remaining on the reticle surface during exposure. The removal of progressive defects requires a number of cleaning process sequences, such as de-pellicle of the reticle, removal of pellicle residue, clean process, recitle inspection, a re-pellicle process and/or a second run of one or more portions of the clean process. The removal of the pellicle residue is very challenging as remaining pellicle on the reticle may damage the reticle and result in scrapping of the reticle.
FIG. 1A depicts a conventional photolithographic system 100. The photolithographic system 100 includes a light source 112 that provides light 114 at a desired wavelength to a surface 108 of a reticle 110. A pellicle 102 may be used to protect the surface 108 of the reticle 110 from particle contamination or other sources of contamination while processing. The pellicle 102 may be supported by a frame 104 at an edge 106 of the reticle 110 at a predetermined distance above the reticle surface 108. The pellicle 102 and the frame 104 may be permanently attached to the reticle 110 or may be removable and replaceable from the reticle 110. The pellicle 102 may be applied, stretched, and attached to the frame 104 with organic adhesives. Adhesives may also be used to attach the frame 104 to the reticle 110. The adhesives along with the pellicle 102 may be typically fabricated from polymers or plastic materials with additives and/or solvents. As the pellicle 102 and adhesives are exposed to radiation or light from the light source 112, the material of the pellicle 102, adhesive and solvents may outgas or evaporate, producing one or more types of residual organic compounds. The outgased organic compounds may further reduce pellicle transparency, cause pellicle thinning and accelerate pellicle photodegradation. Thinning of the pellicle 102 may also cause defects or particle contamination on the reticle 110.
Furthermore, after a number of process has been performed and the pellicle 102 and the frame 104 is removed from the reticle 110, the residual organic compounds may remain on the edge 106 of the reticle 110 where the frame 104 was supported, shown as undesired adhesive residue 150 on the reticle edge 106 in FIG. 1B. Since the adhesive residue 150 may be sticky and viscous, the adhesive residue 150 is difficult to remove from the reticle surface by conventional cleaning techniques, resulting in defects and contamination on the reticle surface.
Therefore, there remains a need for a method and an apparatus to clean adhesive residues on a reticle.